The present invention relates to a filter apparatus, and more particularly, to a filter element for use in a filter apparatus.
A wide variety of filter apparatuses are generally in use for the manufacture of various products including sugar, beer and the like. In one example of such a filter, a plurality of elongated filter elements are placed in parallel in a tank, each element being connected at its lower end to a collecting tube. The filter elements are all spaced substantially equally apart from each other, and a row of filter elements connected together by a common collecting tube is staggered from an adjoining row of filter elements also connected by a common collecting tube.
In filtering operations, it was known to feed the liquid to be filtered from an inlet tube into the tank and fill the tank to a level such that the filtering elements are all submerged in the liquid. The liquid thus passes through the perforated surfaces of each filtering element, flows down to the bottom of the filter element, and reaches the collecting tube. The collecting tubes thus collect the filtrate and transfer it for a further process or step.
One such elongated filtering element includes a plurality of cylindrical filter units stacked coaxially end-to-end with a gasket interposed therebetween adjacent filter units. The top end of the filter element is provided with a top end cap for closing the end opening of the filter element. Likewise, the bottom end of the filter assembly is fixed to a bottom end cap for closing the bottom end opening of the filter element. The bottom end cap has a plurality of openings or apertures for allowing the filtrate to pass therethrough to the collecting tube.
Substantially at the center of both the top end and bottom end caps is fixedly provided a central shaft extending along the axis of the cylindrical filter units and further extending upward beyond the top end cap. The upper end portion of the central shaft is provided with screw threads for connection with a nut. By rotating the nut, the top end cap can be caused to apply compression over the top end of the stack of cylindrical filter units and, at the same time, establish firm connections between the components of filter element.
In the above-described filter element, however, since the central shaft is positioned in the center of the filter assembly there is a considerably large space between the central shaft and the inner wall surface of the stack of cylindrical filter units. In the cleaning operation of the filter element, a reversed air flow from a compressed air source under pressure (approximately 4.5 kg/cm.sup.2), is blown into the interior of the filter units from the bottom apertures (called "backwashing"). In this process, the air under pressure in the first place is used to expand the internal volume of the cylindrical filter units and then at a reduced pressure to operate upon the inner surface. However, the pressure exerted upon the inner surface is not large enough to remove the filter cake deposited upon the outer surface of the filter units or to discharge the filtrate out of the filter units. In addition, a large quantity of air under pressure has been needed for the backwashing purposes. A similar drawback existed with respect to the use of a liquid for reversed liquid flow cleaning operation.
In another aspect, because of the fact that the internal space of the filter element contains a large volume of air, it often happens that after filtering proteinaceous liquids, such as soy sauce, Japanese sake, and beer, black dirt and grime are produced as a result of the contact between the air and the fermentative liquid, and such dirt or grime is apt to become a source of bacterial growth.